I tolerate, more than love, holidays, so I tend to see Clint and Natasha as agreeing with me (no strong connections to any nostalgia/no family to celebrate with/not American...)

But I imagine that Tony, the King of Overcompensation, likes to go ALL FUCKING OUT and basically drowns everyone in all the decorations he can find. Dude would staple a menorah to a Christmas tree, if he could figure out if that's offensive or not.

So when he finds out that Clint and Natasha don't care, he sets out to teach them about the great parts of life they're missing out on.

Mostly, this involves eggnog and claymation.

(I'm Jewish, and I'm pretty sure that's what Christmas is. A bunch of people getting soused on eggnog while they watch Rudolph and there's a tree in there, too.)